| 摘要 |
A mask-wafer bearing an alignment pattern of linear segments extending in a given direction is illuminated obliquely through a patterned mask bearing a symmetrical alignment pattern of linear segments extending in the same direction. A TV camera (25) detects the oblique output beam, the video signal being converted to digital form and temporarily stored. The digital signal corresponding to a mask alignment pattern area is averaged, with removal of the shadow effect resulting from the obliqueness of illumination, and compared with the averaged wafer alignment pattern signal. The resulting signal is employed to displace relatively the mask and wafer for accurate alignment.
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